The basic objective of the study is to provide a reliable estimate of the cost differential in providing medical care to cigarette smokers, former cigarette smokers and non smokers. In 1971 a detailed smoking questionnaire was given to 2,502 members of the Kaiser Foundation Prepaid Health Plan in Portland, Oregon. Detailed records of all ambulatory and inpatient medical utilization have been kept on this population since that time. By relating the original smoking information to subsequent of health services it will be possible to estimate the differential costs of furnishing medical services to individuals and families subdivided by their respective smoking histories. Data will include not only the amount smoked, but also years since cessation in former smokers, the smoking histories of family members of non smokers (so that utilization by non smokers may be linked to the use of cigarettes by other household members), and the length of time current smokers have been smoking. These data can provide the first accurate estimates of the additional costs (if any) of cigarette smoking in the use of medical services.